1. Field of the Invention
The present invention relates to a moving picture compression encoding transceiver apparatus, and in particular to such a moving picture compression encoding transceiver apparatus that transmission bit rate can be concretely estimated even in the case where transmission bit rate is altered step by step.
2. Description of the Related Art
In real time communication for converting a real time video signal and a real time audio signal into digital data and transmitting the digital data, control must be exercised so as to keep the encoding rate in an information source within transmission bit rate.
For example, on radio transmission lines for the like of portable telephones and transmission lines of best effort type such as IP networks, it is considered that transmission bit rate varies every moment according to the congestion situation on the network. If a state in which transmission bit rate is less than the encoding rate in the information source due to this variation continues for a certain fixed time, an increase in delay or an interruption in received video/audio signal occurs and a degradation in communication quality is caused.
In order to prevent the communication quality from falling, it becomes necessary to monitor transmission bit rate, successively reflect the monitored result in control of the encoding bit rate in the information source, and always satisfy conditions required of the real time communication described above.
In the RTCP (Real-time Transport Control Protocol) prescribed in the IETF (Internet Engineering Task Force) RFC 1889, which is now adopted as a substantial international standard scheme, a report packet aiming at monitoring the transmission line is used, and the SR (Sender Report) and the RR (Receiver Report) are defined.
The sender report has an object of providing information serving as a reference in creating a receiver report in a receiver side apparatus. The sender report includes a time stamp, the number of sent media packets (video/audio packets), and the number of sent data bytes. A sender side apparatus periodically transmits sender reports besides actual media packets.
The receiver side apparatus takes out reference time from a sender report transmitted from the sender side apparatus, creates a receiver report on the basis of the reference time, and sends back the receiver report to the sender side apparatus. The receiver report includes a section packet loss factor, the number of accumulated packet losses, a sequence number of a media packet received immediately before, jitter in media packet arrival interval, a time stamp of a sender report received immediately before, and a delay time between reception of an immediately preceding sender report and sending of a receiver report.
In this way, in the conventional media (video/audio) transceiver apparatus adopting the RTCP, sender reports and receiver reports are used, and the sender side apparatus conducts control so as to optimize the receiving quality in the receiver side apparatus by controlling the encoding bit rate of data to be sent and so on, on the basis of a receiver report fed back from the receiver side apparatus.
Information concerning the transmission line that can be estimated in the sender side apparatus by using the RTCP is packet loss caused over a long period of time, packet loss caused over a short period of time, and jitter on the line. This is premised on that in typical wired IP networks (Internet lines) a data bit rate momentarily exceeding the transmission bit rate is acceptable as characteristics of the line at ordinary times, and packet loss and jitter sometimes occur at the time of congestion on the line.
In radio IP networks for portable telephones, however, only estimation of the packet loss and jitter is not sufficient in some cases for a reason described hereafter. For example, in the case of data communication using the third generation portable telephone cdma 2000 1xEV-DO in the sender side apparatus, transmission bit rate (rate mode) in the sending direction of portable telephone is altered among, for example, 9.6 kbps, 19.2 kbps, 38.4 kbps, 76.8 kbps and 153.6 kbps step by step while considering the radio wave state on the terminal side and the congestion state in the base station.
If an encoding bit rate now under transmission exceeds transmission bit rate as a result of alteration of transmission bit rate, the packet loss and jitter increase relatively. Therefore, the sender side apparatus can determine that the encoding bit rate now under transmission needs to be altered, on the basis of the receiver report using the RTCP.
Unlike the Internet line premised on the fixed bit rate even though there is a fluctuation, however, only detection of a change in communication rate is not sufficient in such a network in which stepwise alteration of transmission bit rate is conducted as described above. For example, even if it is known from increase in packet loss or jitter that alteration of the encoding bit rate now under transmission is necessary, which value the bit rate should be altered to is not known. In the case where transmission bit rate has been altered, it is necessary to be capable of rapidly estimating transmission bit rate now in use and finding an encoding bit rate under transmission to be used concretely.